Analog optical signals can be generated using highly-linear directly modulated lasers, such as semiconductor lasers, laser diodes, and the like. In general, the characteristic curves (optical power in mW vs. injection current in mA) (LI curves) of these lasers must be substantially linear and curve or “kink”-free above a threshold current (Is) at which lasing begins. Alternatively, analog optical signals can be generated using externally modulated lasers to compensate, to some extent, for any non-linearity. The overall requirement, using either modulation scheme, is that the generated analog optical signals closely match the input analog electrical signals, without significant distortion. In other words, slope variation compensation must be incorporated in order to maintain a relatively constant extinction ratio of the transmitted analog optical signals.
Non-linearity is caused by, among other things, temperature changes, age, internal parameters, and parasitics. Thus, the directly modulated lasers must be replaced regularly, likely as often as once every few months, as performance degradation occurs. Due to their relatively high cost, this becomes an expensive proposition. This problem is exacerbated by the fact that optical network elements are continually being deployed closer to end users. Thus, these optical network elements are being deployed in uncontrolled “field” environments. Currently, the only “outside-plant” rated components are transceiver-based components for digital communications, not analog communications. Similarly, the externally modulated lasers that compensate, to some extent, for non-linearity suffer from component complexity and are also relatively expensive.
Thus, what are needed are systems and methods for real-time compensation for non-linearity in optical sources for analog signal transmission and the like that minimize component complexity. By providing a correction factor for non-linearity due to temperature changes, age, internal parameters, parasitics, and the like, these systems and methods would eliminate the need for regular laser replacement, and thereby significantly reduce cost.